1. Technical Field of the Invention
This invention relates generally to communication systems and more particularly to RFID systems.
2. Description of Related Art
A radio frequency identification (RFID) system generally includes a reader, also known as an interrogator, and a remote tag, also known as a transponder. Each tag stores identification or other data for use in identifying a person, item, pallet or other object or data related to a characteristic of a person, item, pallet or other object. RFID systems may use active tags that include an internal power source, such as a battery, and/or passive tags that do not contain an internal power source, but instead are remotely powered by the reader.
Communication between the reader and the remote tag is enabled by radio frequency (RF) signals. In general, to access the identification data stored on an RFID tag, the RFID reader generates a modulated RF interrogation signal designed to evoke a modulated RF response from a tag. The RF response from the tag includes the coded data stored in the RFID tag. The RFID reader decodes the coded data to identify or determine the characteristics of a person, item, pallet or other object associated with the RFID tag. For passive tags, the RFID reader also generates an unmodulated, continuous wave (CW) signal to activate and power the tag during data transfer.
RFID systems typically employ either far field or near field technology. In far field technology, the distance between the RFID reader and the tag is great compared to the wavelength of the carrier signal. Typically, far field technology uses carrier signals in the ultra high frequency or microwave frequency ranges. In far-field applications, the RFID reader generates and transmits an RF signal via an antenna to all tags within range of the antenna. One or more of the tags that receive the RF signal responds to the reader using a backscattering technique in which the tags modulate and reflect the received RF signal.
In near-field technology, the operating distance is usually less than one wavelength of the carrier signal. Thus, the reading range is approximately limited to 20 cm or less depending on the frequency. In near field applications, the RFID reader and tag communicate via electromagnetic or inductive coupling between corresponding reader and tag coil antennas. Typically, the near field technology uses carrier signals in the low frequency range.
The International Organization for Standardization (ISO) has developed an RFID standard called the ISO 18000 series. The ISO 18000 series standard describes air interface protocols for RFID systems especially in applications used to track items in a supply chain. The ISO 18000 series has seven parts to cover the major frequencies used in RFID systems around the world. The seven parts are:    18000-1: Generic parameters for air interfaces for globally accepted frequencies;    18000-2: Air interface for below 135 KHz;    18000-3: Air interface for 13.56 MHz;    18000-4: Air interface for 2.45 GHz;    18000-5: Air interface for 5.8 GHz;    18000-6: Air interface for 860 MHz to 930 MHz;    18000-7: Air interface at 433.92 MHz.
According to the ISO 18000-2 and 18000-3 parts of the ISO 18000 series, near-field technology with magnetic/inductive coupling has an air interface protocol at low frequency (LF) of 135 KHz or less or at 13.56 MHz high frequency (HF). The communication protocol used by the reader and the tag is typically a load modulation technique.
Far field technology with RF coupling has three ISO defined air interfaces at 2.45 GHz microwave frequency according to ISO 18000-5, 860 MHZ to 930 MHz ultra high frequency (UHF) range according to ISO 18000-6 and 433.92 MHz UHF according to ISO 18000-7. For UHF at 860-930 MHz, the ISO 18000-6 has defined two tag types, Type A and Type B with a reader to tag link defined as including either 33 kbps or 40 kbps data rate, Amplitude Shift Keying (ASK) modulation, and biphase-space (FM0) encoding of data.
In addition, the EPCglobal Class 1, Generation 2 standard defines a tag standard using UHF with a tag to reader link of 40 to 640 kbps, ASK or Phase Shift Keying (PSK) modulation and data encoding of biphase space (FM0) or Miller-modulated subcarrier.
Generally, RFID readers employing near field technology operating at LF or HF have been used in applications involving reading item-level tagging for inventory control in the supply chain management or applications involving short range reads such as smart cards or vicinity credit cards, e.g. for access control or monetary use, passports, money bills authentication, bank documents, etc. Such applications do not need long range reads of the tags but may need more security provided by near field technology. In addition, near field technology is known for better performance for reading of tags near fluids, such as fluid medications, wherein far field RF coupling tends to incur interference from the fluids.
RFID readers employing far field technology RF coupling at microwave or UHF have been used to read tags in applications involving shipping units such as pallets or carton level tracking or other applications needing long-distance reads.
Currently, an RFID reader may consist of a controller or microprocessor implemented on a CMOS integrated circuit and a radio implemented on one or more separate CMOS, BiCMOS or GaAs integrated circuits that are uniquely designed for optimal signal processing in a particular technology (e.g., near-field or far-field), but not in both. These different types of technology and the number of different RFID standards, each defining a different protocol for enabling communication between the reader and the tag, has inhibited the wide spread use of RFID readers for multiple applications.